The present invention concerns improvements upon arrangements for adjusting the mass of the gobs of thermoplastic material, especially molten glass, which are severed one after the other off a cord of such material issuing from a feeder, the gobs being fed into the mold of a molding machine and deformed in so-called positive manner by means of a pressing member which penetrates into the gobs. In such arrangements, the maximum penetration depth achieved by the pressing member during each molding-machine operating cycle is mechanically detected by a distance transducer, the latter being connected to a metallic actuating element for a differential transformer at whose output is produced an electrical signal proportional to the respective maximum penetration depth, the signal being applied to a regulating circuit for control of a dosing structure which adjusts the mass of the gobs.
U.S. Pat. No. 3,180,718, in FIGS. 8 and 9 thereof, discloses an arrangement of this type. In this arrangement, use is made of a differential transformer having a primary winding and two secondary windings. Each of these windings is embedded in a respective external peripheral groove of a stationary inlet pipe for the cooling air used to cool the pressing members, these inlet pipes being made of electrically insulating material. The pressing member is secured on a pipe-shaped piston rod made of metal, the free end of which surrounds the inlet pipe and serves as an actuating element. When the piston rod moves relative to the windings, the differential transformer produces a variable output signal which is proportional to the movement of the pressing member and which constitutes a measure both of this movement and also of the penetration depth of the pressing member. Such output signal is preferably displayed and/or recorded; additionally, however, this output signal is supposed to be used in the monitoring and/or control of the variables employed to monitor and/or control the size of the charged gobs. However, the publication in question discloses no details concerning how such monitoring or control action could be implemented.
In the older Federal Republic of Germany published patent application DE-OS No. 29 23 705, it is proposed, for I.S.-glass-forming machines, that one measure the end region of the distance through which moves the actuating piston of the pressing member or the piston rod of the actuating piston. The traversed distance is supposed to be detected by means of a measurement transducer and displayed. This is supposed to be made to occur, for example, by means of several electrical contacts arranged in the path of such movement, the electrical contacts being sensed or engaged one after the next. In the publication in question, mention is also made of the possibility of using the values detected by the measurement transducer for regulating the size of the glass gobs fed to the gathering mold, e.g. by displacement of the severing mechanism which severs the gobs from off the cord. However, details of such a regulating mechanism are not set forth.